The present invention relates generally to underwater diving masks, and, more particularly, to a lens system that compensates for the magnification problem caused by the different indices of refraction between water and air.
Underwater diving masks are commonly used in a variety of underwater activities, such as scuba diving, snorkeling, underwater photography and the like. Conventional diving masks generally consist of a pre-formed face piece that fits over the diver""s eyes and generally also the nose, and a strap that secures the face piece against the diver""s face. Some diving masks have a single large opening formed in the forward part of the face piece, and a relatively flat transparent plate is mounted in the opening to enable the diver to view the surrounding marine environment. In other diving masks, two openings are formed in a side-by-side relationship in the forward part of the face piece (i.e. one for each eye of the diver), and a flat transparent plate is mounted in each opening.
While conventional diving masks serve the basic function of keeping water away from the diver""s eyes, they have a number of disadvantages which are well known in the art. Most notably, because marine light is bent as it passes through the flat plate due to the different indices of refraction between water and air, objects viewed on an axis perpendicular to the plate appear approximately 33% larger and 25% closer than they actually are. The magnification of objects viewed off-axis is even larger. As a result, small objects in the water can be magnified out of proportion to their size, which can cloud the visual field. In addition, the diver""s peripheral vision is severely compromised, resulting in what is commonly referred to as xe2x80x9ctunnel vision.xe2x80x9d
The magnification problem associated with conventional diving masks has been addressed in the past by the use of complex lens systems. For example, U.S. Pat. No. 3,672,750 to Hagen discloses an underwater diving mask wherein a diver is required to look through several layers of material that have a refractive boundary between them. Another example is the underwater diving mask disclosed in U.S. Pat. Nos. 5,764,332 and 5,625,425 to Kranhouse, wherein the spherical centers of two hemispherically-shaped lenses are designed to coincide with the optical nodal points of the diver""s eyes. While these diving masks purportedly compensate for the foreshortening effect of the water, their complex designs make them relatively difficult and expensive to manufacture. A further problem associated with the Kranhouse diving mask is the relatively large size (and thus weight) of the lenses, which makes the mask impractical for use by dry-suit divers who generally require lenses formed of tempered glass.
Another attempt to compensate for the different indices of refraction between water and air is shown in U.S. Pat. Nos. 5,359,371 and 5,523,804 to Nolan, the applicant of the present application. In these patents, an underwater diving mask is disclosed which includes a lens having a flat inner surface facing toward the diver""s face and a concave outer surface facing away from the diver""s face. Because the outer surface of the lens is concave (as opposed to flat), marine light intersects the lens normally and is transmitted therethrough without deviation.
In addition to the above-noted magnification problem, there are other disadvantages associated with conventional diving masks. For example, the air chamber between the support plate and the diver""s face can easily fog up when the diver exhales through his or her nose. Another problem is that approximately 11% of marine light is reflected off the support plate, resulting in a visual field that appears dim to the eyes of the diver. Also, the diver""s vision is compromised due to the fact that red and yellow hues are rapidly absorbed at 1-1.5 atmospheres. In addition, certain commercial and military activities (e.g. underwater gas and arc welding operations) can place divers at risk to radiation emissions that can pass through the support plate and have a deleterious effect on the nonregenerative ocular tissue of the divers""eyes.
Therefore, in view of the problems associated with the above-described diving masks, it is an object of the present invention to provide a diving mask having a lens system that 1) is designed to compensate for the different indices of refraction between water and air, 2) has a simple design that it is relatively easy and inexpensive to manufacture, 3) inhibits fogging, 4) reduces the amount of marine light reflected off the lens, 5) provides uncompromised vision, and 6) protects divers from the harmful effects of underwater radiation emissions.
These and other objectives are met by the plano-convex lens system for the underwater diving mask of the present invention. This diving mask generally consists of a face piece formed of suitable material so as to substantially conform to the contour of a diver""s face, and a strap for releasably securing the face piece against the diver""s face. The face piece has at least one opening formed in the forward part thereof for receiving a lens therein. The inner surface of the lens facing toward the diver""s face is substantially flat (i.e. planar), and the outer surface of the lens facing away from the diver""s face is slightly convex.
Preferably, the diopter value of the outer surface of the lens is between 0 and 1.0, and is most preferably between 0 and 0.5. These diopter values are sufficient to compensate for the magnification problem caused by the different indices of refraction between water and air, while remaining well out of range of the diopter values used for corrective vision. A secondary corrective lens can, however, be affixed to the flat inner surface of the lens for those divers who would otherwise require corrective lenses.
In one embodiment, the diving mask has a single large opening formed in the forward part of the face piece, and a large plano-convex lens is mounted within the opening to provide a closure therefor. In another embodiment, the diving mask has a single large opening formed in the forward part of the face piece, and a large transparent support plate is mounted within the opening to provide a closure therefor. The support plate itself is substantially flat on both sides, with the exception of a pair of plano-convex lenses integrally formed in a side-by-side relationship within the plate (i.e. a lens for each eye of the diver). In yet another embodiment, two openings are formed in a side-by-side relationship in the forward part of the face piece (i.e. an opening for each eye of the diver), and a plano-convex lens is mounted within each opening to provide a closure therefor.
The underwater diving mask of the present invention is also preferably designed to overcome other problems associated with conventional diving masks. For example, anti-fogging means may be applied to the inner surfaces of the plano-convex lenses to inhibit fogging. Also, an anti-reflectant coating may be applied to the plano-convex lenses for boosting the light transmission from 89% to 99.2%. In addition, to provide enhanced contrast imaging and/or protect the diver from ionizing and non-ionizing radiation emissions associated with dangerous underwater work (such as gas and arc welding operations), the plano-convex lenses may be treated or coated with a coloring agent to inhibit the passage therethrough of certain wavelengths of light. The plano-convex lenses may be polarized for this same purpose.
The present invention will be better understood from the following detailed description of the invention, read in connection with the drawings as hereinafter described.